1. Field of the Invention
The present invention relates to a charged particle beam apparatus which employs a scanning electron microscope (SEM) to inspect particles and/or defects on a sample surface. More particularly, it relates to a low-voltage scanning electron microscope (LVSEM) for inspecting particles and/or defects on surfaces of wafers or masks in semiconductor manufacturing industry.
2. Description of the Prior Art
In semiconductor manufacturing industry, sometime particles appear and remain on surfaces of masks and/or wafers during semiconductor fabrication process for some reasons, which impact the yield to a great degree. To monitor and therefore ensure the yield, optical apparatuses or called optical tools which are typically based on microscopy, have been employed to inspect particles after some fabrication processes because of their high inspection throughput and a good detection efficiency. As integrations of IC chips are required higher and higher, critical dimensions of patterns on wafer and mask are shrunk, and consequently smaller and smaller particles become killers in the yield. On development trends, optical tools are losing their abilities to detect killer particles due to their longer wavelengths relative to particle dimensions.
Theoretically, an electron beam (e-beam) has a relatively shorter wavelength (such as 0.027 nm/2 keV) relative to particle dimensions (down to several nm), and therefore can provide higher detection sensitivity for small particles than an optical beam. Higher detection efficiency comes from higher detection sensitivity. Conventional e-beam apparatuses or called e-beam tools for inspecting defects on wafer/mask, which are based on Low-voltage Scanning Electron Microscopy (LVSEM), can directly perform particle inspection. However they are always criticized for low throughput. A large beam current is necessary to get a high throughput, but incurs strong Coulomb Effect which impacts the image resolution and thereby reducing the sensitivity.
Accordingly, a new-type e-beam tool especially for small particle inspection, which can provide high detection efficiency and high inspection throughput, is needed. In addition, it will be advantageous if the tool can perform defect inspection as well.